It is advantageous for commercial users of electrical components to be able to purchase much used components in large quantities, for later use as needed. To facilitate these large purchases, suppliers sometimes package components by mounting them between long tapes wound on spools or reels, which are easily stored by the purchasers, and from which the components are easily accessible.
In industrial applications, components are advantageously positioned physically on circuit boards with their conductors extending through holes in conductive patterns on the boards, to which patterns they are connected by wave soldering. This means that the solderability of the component conductors must be good at the time of use, regardless of how long a period of storage has occurred.
Various suppliers use various finishes on the component conductors, however: coatings of gold, silver, and tin are known, which may be of different thicknesses, porosities, and surface contamination. It has been found that a considerable amount of "touch up" action is often required after wave soldering, to perfect connections which were not made satisfactorily, and this is an expensive, manual process. The period of storage between purchase and use also has an unpredictable affect on the solderability of the component's conductors.
One way of overcoming this is to hand-tin all the conductors as the components are taken from the storage reels and before they are mounted on the circuit boards, but this is also a very costly and time consuming process.